You can't really fix stunting. Discus grow like crazy for a couple of years, then really slow down, and if you get to a year or so and the fish aren't grown, then that's it, they're stunted, and you can't do to much to fix it. What that means is that to a purist they won't look that good, but they can still make nice pets. They won't live as long, for very stunted fish 5 years is decent going ompared to 10+ for a grown adult, but that's still a while. You need to commit to keeping them in clean, warm water so get a heater set it high and say hello to water changes.